JPS641174B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a novel electrolyte. Currently, the production of chlorine and caustic soda through salt electrolysis, the electrolysis industry such as aluminum smelting, and various batteries such as manganese dry batteries and lead-acid batteries are becoming important industries. In addition, various electrochemical measurements such as PH measurement are becoming increasingly important. Recently, methods for effectively utilizing solar energy have been deepened, and the superiority of electrochemical methods has begun to be recognized, and organic electrolysis methods are being considered as a new method for producing organic compounds. However, conventional electrochemical systems use water or highly polar organic solvents as solvents, and there are no known electrochemical systems that use nonpolar or low polarity solvents. As a result of careful study of the function of this crown compound, the present inventors discovered that it is possible to construct a completely new electrochemical system different from conventional electrochemical systems using this compound. That is, in conventional electrochemical systems, the role of the electrolyte was simply a dispersion medium for the electrode active material that had ionic conductivity, but in the present invention, the role of the electrolyte was a solution of a crown compound holding cations and a low polar solvent. including;
In the electrolytic solution characterized by substantially not containing a polar solvent, the electrolytic solution containing the crown compound itself includes cations and selectively solubilizes ions or salts, thereby achieving the unique functions of the crown compound. It also makes it possible to utilize the features of low polarity or nonpolar solvents, which were impossible to use in conventional electrochemical systems. That is, the present invention does not contain polar solvents, does not have the disadvantages associated with polar solvents, and allows for a number of completely new electrochemistry systems that cannot be implemented or realized in conventional electrochemical systems due to the characteristics of the solvent itself. This is the first time that a practical method has become practicable. A specific example of such a completely new electrolytic solution will be explained below. (A) A novel electrical system using inexpensive and stable anode materials. In conventional electrochemical systems, water or highly polar organic solvents were used as the electrolyte (solvent), and expensive metals such as platinum had to be used as electrode materials for reasons such as stability. In other words, although there has traditionally been a desire to increase anode stability by using nonpolar or low polarity solvents and to use many inexpensive metals as electrodes, supporting salts are not soluble in these solvents. Because of this, it was not possible to increase the ionic conductivity of the solution, making it unsuitable for use as an electrolyte. The inventors of the present invention have made extensive studies to find out whether this non-polar or low-polar solvent can also be used as an electrochemical solvent, and have discovered that an electrolyte can be created by using a crown compound together with a non-polar or low-polar solvent. discovered and achieved the present invention. The metal electrode that can be newly used in the electrolytic solution according to the present invention may be any metal electrode as long as it is extremely difficult to form a complex between the cation of the constituent metal and the crown compound used. At this time, the dissolution of the electrode itself is suppressed, and the potential range, which was previously limited by the dissolution potential of the metal in the solvent, is expanded to the decomposition potential of supporting salts and crown compounds, making it possible to perform electrolysis in a wide potential range. It is possible to make the electrode possible. For example, when using a (15-crown-5)-benzene mixed solvent and sodium tetraphenylborate as a supporting salt, the added
Metals other than (a), (a) and silver that are known to form stable complexes with 15-crown-5, preferably first transition metals,
More preferred are copper, zinc, iron, and alloys thereof. (B) A new metal refining method that controls the metal elution potential The electrolyte used in conventional wet metal refining uses water or a highly polar organic solvent as a solvent, and the elution order of metals is controlled. is a direct reflection of the normal ionization tendency. However, in the electrolytic solution according to the present invention, the electrolytic solution itself may strongly reflect the cation inclusion property of the crown compound, and as a result, the elution order of metals can be reversed from the normal order of ionization tendency. Therefore, metals that were conventionally found in abundance in the anode mud can be made to exist in abundance in the electrolyte. The target metal can be extracted with high purity from the electrolyte thus obtained by direct solvent extraction or by the reverse process of anodic elution (cathode deposition). As described above, we have invented a metal refining method that is completely different from conventional methods. Further, according to the present invention, all metals that can be included in crown compounds such as Group 1 metals such as gold and silver, Group 8 metals such as platinum, palladium, and rhodium, and uranium can be refined. (C) Application to organic electrolysis In conventional electrolytes, water or highly polar organic solvents are used as the electrolyte, and special solvents such as cellosolve are used when electrolyzing polyacene, etc. The current situation was that it was extremely difficult to regulate the electric potential accurately. Organic synthesis methods that originally rely on electrolysis can selectively perform specific oxidation and reduction reactions under potential regulation conditions, and conventionally electrolysis is performed under potential regulation conditions. Polyacenes, which could not be produced, are chemical species that have many possibilities as medical raw materials. Therefore, a technique for carrying out electrolytic reactions of these chemical species under potential regulation has been widely required from the viewpoint of high value-added electrolytic synthesis. On the other hand, in the electrolytic solution according to the present invention, the silver wire reference functions relatively stably due to the ion selectivity of the crown compound, and at the same time, the characteristics of a low polarity or non-polar solvent are maintained, which makes it difficult to use conventional electrolytic technology. In this case, polyacene, etc., which could not be electrolyzed under potential regulation conditions, can be electrolyzed under potential regulation conditions. Furthermore, when performing organic electrosynthesis, the choice of solvent affects the product. For example, 1,
In the electrolytic oxidation reaction of 2, 3, 4, 5-tetra-methylbanyene, the products are different as shown below.
This is closely related to the stability of cations produced by the reaction. {K.Nyberg, Chem.Commun., 774 (1969)} When a complex of a cation and a crown compound or a naked anion is present in a low polar solvent as in the case of the present invention, the product can be selectively produced by an anion substitution reaction depending on the type of anion, the solvent used, etc. Alternatively, it is conceivable that a dimerization reaction or the like may occur. (D) Application to semiconductor wet photovoltaic cells Recently, ways to effectively utilize solar energy have been explored, and the superiority of electrochemical methods has been recognized. In order to realize the utilization of solar energy by semiconductor wet photovoltaic cells, at least the following matters must be solved. (1) Improving energy conversion efficiency, (2) Establishing a cheap and simple manufacturing method for semiconductor materials, (3) Suppressing semiconductor electrode melting.On the other hand, semiconductor electrode materials that meet the conditions (1) and (2) above are , CdS, and many others have been known so far. However, as will be described later, the semiconductor electrode tends to melt, and in order to assemble a highly efficient photovoltaic cell, suppressing the melting of the semiconductor electrode is an essential condition. Thus, the electrolytic solution according to the present invention has been found to have a remarkable effect on suppressing the formation of semiconductor electrodes, which is currently the most sought-after problem (3). First, the operating principle of a semiconductor wet photovoltaic cell and conventional techniques for suppressing electrode dissolution will be explained. TiO ₂ is an example of a semiconductor wet photovoltaic cell that has a large band gap of 3.0 eV and is an example of an electrode that is stable against self-dissolution reactions in a photoexcited state.
An example will be explained in which a semiconductor photoanode is in contact with an aqueous electrolyte. For example, when TiO ₂ , an n-type semiconductor, is used as an electrode and placed in an electrolytic solution, a region with a potential gradient called a space charge layer is created on the semiconductor surface. As can be seen in FIG. 1, this space charge layer portion exhibits a structure similar to the pn junction portion in a solar cell, and it is understood that it will perform a similar function. That is, at this interface, separation of electrons and holes generated by photoexcitation occurs, that is, a photovoltaic force is generated, and when the circuit is closed, a photocurrent flows. At the same time, as an electrode reaction, the observed occurrence of water oxidation may occur on the TiO ₂ electrode side, and hydrogen generation corresponding to the reduction of protons may occur on the platinum side. As mentioned above, in this semiconductor wet photovoltaic cell,
In addition to electrical energy, products such as hydrogen can be obtained as a result of the battery reaction. However, TiO ₂ has a band gap of 3.0 eV, so it only responds to light in the wavelength range close to ultraviolet. In order to capture as much solar energy as possible, it is necessary to use a semiconductor with a narrower bandgap than TiO ₂ . In reality, it is said that a semiconductor with a voltage of 1.1 to 1.4 eV is optimal considering the spectral distribution of sunlight. But for example
Si (1.1eV) has problems such as the tendency to form an insulating oxide film on the surface in solution and the photovoltaic force value is low. As shown in Table 1, various semiconductors are currently being studied for photoelectrode reactions. As is clear from this table, CdS, CdSe,
Compound semiconductors such as GaP and GaAs have a wide photosensitive range and have the potential to utilize solar energy more effectively. However, these n-type semiconductors cause the following dissolution reaction of the semiconductor itself under light irradiation in a normal electrolytic solution. CdS+2p ⁺ →Cd ²⁺ +S (1) CdSe+2p ⁺ →Cd ²⁺ +Se (2) GaP+6p ⁺ +3H ₂ O→Ga ³⁺ +H ₃ PO ₃ +3H ⁺ (3) GaAs+6p ⁺ +3H ₂ O→Ga ³⁺ +H ₃ AsO ₃ +3H ⁺
(Four)

[Table] The theory regarding the stability and instability of semiconductor anodes in semiconductor wet photovoltaic cells was developed in 1977 by West German Gerritscher and American Bird.
Wrighton et al. discovered that the relationship between the decomposition potential of a semiconductor and the oxidation potential of a redox agent, such as water, plays an important role, and the results shown in FIG. 2 were submitted. In order to use CdS as an electrode for electrochemical optical cells, it is necessary to be able to suppress its dissolution reaction. There have been various attempts to achieve this, but the most well-researched method has been to use holes generated by photoexcitation to preferentially react with chemical species added to the electrolyte, rather than involving them in the dissolution reaction. This is a way to avoid it. CdS and
For CdSe, its chemical species are S ^2- , Se ^2- ,
Chalcogenide reducing agents such as Te ^2-
As extensively studied by Wrighton et al., Table 2
The results shown below have been reported. (J.Am.
Chem.SoC.99, 2839, 1977 and 99, 2834,
(1977) In this case, on the semiconductor surface, reactions (1) to (4)
A competitive reaction with reaction (5) shown below occurs, and the reaction
When (5) occurs almost completely preferentially,
It is said to be ``stable,'' but when some dissolution reactions are occurring, it is said to be ``unstable.'' Red＋np ⁺ →OX ⁿ⁺ (5)

[Table] The present inventors have previously conducted research on stabilizing this unstable electrode and were able to determine what kind of redox potential an effective reducing agent has. (T.Inoue, T.Watanabe, A.
Fujishima, K. Honda, K. Kohayakawa, J.
Electrochem.Soc., 124, 719 (1977)) As a result, as shown in Figure 3, taking a CdS single crystal electrode as an example, reaction (1) and reaction (5) on the CdS single crystal electrode are The competitive reaction of changes with the redox potential and is a strong reducing agent.
It can be seen that the effect of suppressing the dissolution of CdS is large. From this result, as shown in FIG. 4, the potential of the redox agent capable of suppressing CcS dissolution needs to be above the dissolution potential. At the same time, the maximum theoretical circuit voltage of this semiconductor wet photovoltaic cell in a photoexcited state is |E _CB −ED _| . The above is the technology related to the stabilization of semiconductor wet batteries that has been used in the past, but this method is
As shown in Table 2, it is essential to add a significantly colored reducing agent to the electrolytic solution system, resulting in an unavoidable loss from the viewpoint of effective utilization of light energy. In addition, the maximum theoretical value of the open circuit electromotive voltage in the photoexcited state of a semiconductor wet photovoltaic cell is |
It does not exceed Ered/oX−E _D |. On the other hand, the electrolytic solution according to the present invention uses a completely different mechanism from the conventional one when stabilizing the semiconductor photoanode of the semiconductor wet photovoltaic cell. That is, in the conventional stabilization system of a semiconductor wet photovoltaic cell, the role of the electrolytic solution was merely a dispersion medium for the electrode active material having ionic conductivity. On the other hand, in the system for stabilizing a semiconductor wet photovoltaic cell using the electrolyte according to the present invention, the electrolyte itself is
As a result, it has functions unique to crown compounds, such as selectively including cations or salts in crown compounds and solubilizing them.
When MnXm is used as a semiconductor composition, MnXm〓
nM〓 ⁺ (Solv) mX＋n〓 ED defined by △G of ^e-
However, it strongly reflects the stability of M〓 ⁺ (Solv), that is, the stability of the complex between the crown compound and the metal cation constituting the semiconductor, and as a result moves in a significantly noble direction. As a result, unlike conventional methods, significant electrode stabilization was observed even without the addition of colored reducing agents, etc., and the condition of complete electrode stabilization, that is, E _p > E _VB , was not achieved. Even in this case, the open circuit voltage in the photoexcited state of the semiconductor wet photovoltaic cell increases because the E _D is significantly more noble than in the conventional system, and the range of selection of the redox potential of the additive reducing agent is expanded. could be improved over the stabilization conditions of conventional semiconductor wet photovoltaic cells. In summary, the stabilization of semiconductor photoanodes, which was an essential issue in semiconductor wet photovoltaic cells, has been solved by employing the novel electrolyte according to the present invention. (E) Application to non-aqueous battery systems With the recent development of electronics, it is desired to develop batteries with high energy density. Batteries using lithium or sodium as the negative electrode are
Due to their large ionization tendency and high energy density, some of them have already been put into practical use. Conventionally used electrolytes include propylene carbonate, r-butyrolactone, dimethylformamide, and tetrahydrofuran because of their aprotic high ionic conductivity. However, the anode active material
Lithium batteries using CuF ₂ , CuCl ₂ , etc. have been widely studied, but for example, copper fluoride (CuF ₂ )
-The utilization rate of lithium batteries decreases significantly as the discharge current increases. Furthermore, CuF ₂ has a high solubility in organic electrolytes and is extremely sensitive to impurities such as water. As a result, batteries using LiClO ₄ -PC electrolyte have a short shelf life.
There are reports that when stored at ℃, the battery completely self-discharges after several months. Copper chloride (CuCl ₂ )-lithium batteries also
CuCl ₂ has a higher solubility than CuF ₂ and self-discharge became a problem. Attempts have been made to investigate the common ion effect caused by the coexistence of excess AlCl ₃ or the use of ion exchange membranes, but without success. Discharges of fairly high currents are possible over a wide temperature range, but the discharge curves are unstable. However, if the electrolyte is changed to a mixture of a cation-crown complex (containing an excess of free crown compounds) and a small amount of tetrahydrofuran, for example, the dissolution of copper fluoride and copper chloride in the organic electrolyte becomes smaller, resulting in a lower utilization rate. can be maintained at a high level, significantly extending the shelf life of the battery. Although specific examples of the electrolytic solution of the present invention have been illustrated above, by using a solution of a crown compound that retains cations and a low polar solvent as the electrolytic solution or a part thereof, it is possible to solve problems that were previously difficult or impossible. It has enabled a variety of electrochemical reactions, resulting in many effective and novel methods for the effective conversion of solar energy, the use of inexpensive electrode materials, the simple refining of precious metals, and the production of high-power batteries. I was able to develop it. In the present invention, crown compounds are a group of compounds that have a heterocyclic structure with oxygen or oxygen and nitrogen and/or sulfur as electronic atoms, and have the ability to incorporate cations into the vacancies of the ring to form a complex. It refers to a compound, and also includes non-reduced hetero compound analogs having such abilities. Typical examples of these crown compounds include CJ
Pedereen J.Amer.Chem.Soc., 89 , 7017 (1967)
A group of macrocyclic polyethers called crown ethers and their derivatives reported in J.M.Lehn
There is a group of bicyclic polyethers and their analogues with a nitrogen bridgehead atom called cryptands, which were reported by J. J. Christensen in Structure and Bonding, 16 , 1 (1973), and their analogs.
DJE―atough, RMIzatt Chem.Revs., 74 ,
351 (1974), there are heterocyclic compounds that are collectively referred to as crown compounds. Examples of the structures of these crown compounds are as follows (), (), (), (), (),
and so on. here,

[Formula] (X=H, -CH ₃ or -C ₂ H ₅ , m=2-4) D=O, N and or S,
n=4-10. Here, R is the same as R in (), m = 1 to 4, n = 4 to 10, D = O, N and or S,

【formula】

【formula】

【formula】

【formula】

[Formula] or

[Formula]. Here, R ¹ and R ² are the same as R in (), and R ¹
and R ² may be the same or different. D
=O, N and/or S, A and B are the same as A in (), and A and B may be the same or different. Moreover, m=0-4, and n=1-4. Here, l, m, and n are integers of 0 to 2. () R ¹ ―O(―R ² ―O―)― _o R ^1Here , R ¹ is ―CH ₃ , ―C ₂ H ₅ ,

【formula】

[Formula], and R ² is the same as R in (), and n=3 to 9. The ability of such a crown compound to incorporate a cation into the vacancy of its ring to form a complex depends on the type and number of electron-donating atoms present in the ring, the size of the ring (i.e., the number of ring members), and the cation. It is determined by factors such as the ionic diameter of the ion, and therefore the numerical values and substituents corresponding to l, m, n, D, R, R ¹ , R ₂ , A, and B in the above general formula are determined by the respective general formula. It is preferably within the range described above, and is preferably selected depending on the cationic species (of the supporting salt) used in the present invention. Specific examples of crown compounds include the following: In the following specific example(),
Those belonging to () and () are mainly based on the crown names proposed by Pedersen in the above-mentioned paper and currently commonly used. number of atoms (i.e., number of ring members)] - [Crown (An azacrown is composed of oxygen and nitrogen as electron-donating atoms, a thiacrown is composed of oxygen and sulfur, and a thiacrown is composed of oxygen, nitrogen, and sulfur. (Azathia crown) - [Number of electron-donating atoms present in the ring].
In other words, those belonging to () are 12-crown-4, 14-crown-4, 15-crown-5,
18-Crown-6,18-Zia the Crown-6,18
―Jitia Crown―6,18―Azachia Crown―
6. Contains propylene oxide cyclic tetramer, etc.
Those belonging to () include benzo-15-crown-5, benzo-18-crown-6, methylbenzo-18-crown-6, cyclohexyl-18-crown-6, benzo-18-azacrown-6,

【formula】

[Formula] etc., and those belonging to () include dibenzo-15-crown-5, dicyclohexyl-15-
Crown-5, Dibenzo-18-Crown-6, Dibenzo-24-Crown-8, Dimethyldibenzo-
30-crown-10, dicyclohexyl-18-crown-6,

【formula】

【formula】

[Formula] etc. are included. A specific example of something belonging to () was proposed by Lehn in the above paper and is now commonly used using the name of cryptand, namely [creeptand] - [the number of oxygen atoms present in each of the three chains]. If shown, cryptand [2, 2, 1], cryptand [2, 2, 2], cryptand [3, 3, 3], etc. are included. Those belonging to () include tetraethylene glycol dimethoxy ether, pentaethylene glycol dimethoxy ether, tetrapropylene glycol dimethoxy ether, etc. Although these are acyclic compounds, electron-donating oxygen atoms present in the chain It coordinates around a cation and exhibits substantially the same behavior as a heterocyclic compound. The crown compound used in the present invention is as described above.
It can be synthesized according to the method described in Pedersen, Lehn, Christensen et al. In the present invention, the cations and their counter anions that are used and retained in the crown compound are as follows. As cations, group (a) atoms of the periodic table (Li, Na, K, Rb, Cs), group (a) atoms (Mg,
Ca, Sr, Ba) and _NH4 ⁺ are used. The counter anion must be soluble in the electrolyte of the present invention, and must be ionically dissociated to some extent.
A material with electrical conductivity is used. Specifically, I ^- ,
SCN ^- , PF ₆ ^- , ClO ₄ ^- , RCOO ^- , Pirate,
BF ₆ ^- , BR ₄ ^- (R is a hydrogen atom or has 1 to 12 carbon atoms
aliphatic or aromatic hydrocarbon residues), AlCl ₄ ^- , etc. The low polar solvent used in the present invention includes so-called non-polar solvents, and includes saturated aliphatic hydrocarbons, aromatic hydrocarbons, unsaturated hydrocarbons, halogen hydrocarbons, and ether compounds. Saturated aliphatic hydrocarbons include cyclopentane, pentane, 2-methylbutane, 2,2-dimethylpropane, methylcyclopentane, cyclohexane, hexane, methylpentane, dimethylbutane, methylcyclohexane, heptane, methylhexane, dimethylpentane, and ethyl. Cyclohexane, octane, etc. Aromatic hydrocarbons include benzene, toluene, O
-xylene, m-xylene, p-xylene, ethylbenzene, cumene, mesitylene, etc. Examples of unsaturated hydrocarbons include pentene, hexene, octene, cyclohexene, and styrene. Examples of halogenated hydrocarbons include carbon tetrachloride, chloroform, chlorobenzene, fluorobenzene, fluorotoluene, bromobenzene, and bromoform. Examples of the ether compound include 1,4-dioxane, diphenyl ether, diethyl ether, dimethyl ether, ethyl methyl ether, tetrahydrofuran, anisole, and dimethoxyethane. In the present invention, the mixing ratio of the crown compound that retains cations and the low polar solvent varies depending on the expected conductivity of the electrolyte, the solubility of the crown compound, etc., but is generally a molar ratio of 99 to 10:1 to 90. It is. The electrolytic solution of the present invention can be prepared using conventional methods for preparing a cation-retaining crown compound, such as dissolving a supporting salt having appropriate cations and counteranions in a solution of a crown compound and a low polar solvent. Adopted. The present invention will be explained below with reference to Examples. Example 1 First, 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane), whose pore radius is approximately equal to the ionic radius of sodium, was used as a crown compound, and a low polar solvent was used. The dielectric constants of solutions with different mixing ratios of benzene and benzene were measured. The measurement system uses a three-pole measurement container including a guard electrode, inputs a 1KHz sine wave, uses a Lock-in Amp as a detector, and balances the bridge to measure conductivity and capacitance. did. The dielectric constant of the solution was determined from the ratio of the empty capacity of the measurement container to the measured capacitance. The measurement results are shown in Figure 5. Next, using a solution with a dielectric constant of 5.7 in which the molar fraction of benzene was fixed at 0.8, sodium tetraphenylborate was gradually added to this solution as a supporting salt, and the electrical conductivity changed at that time. I looked into it. The measurement is carried out using a 1K conductivity measuring container with platinum black electrodes.
This was done by inputting a Hz sine wave and balancing the bridge. The measurement results are shown in Figure 6. When the added salt concentration is 0.1M, the electrical conductivity is 2.8×
It became 10 ^-4 ohm ^-1 cm ^-1 . 10 -3 M is added to a solution with an electrical conductivity of 2.8 × 10 ^-4 ohm ^-1 cm ^{-1, which} is obtained by adding 0.1 M sodium titraphenylborate to a solution with a benzene molar fraction of 0.8 and a dielectric constant of 5.7. of ferrocene was added as a redox agent, a silver wire was used as a reference electrode, and a cyclic voltammogram was measured using a platinum wire as a working electrode and a counter electrode. The results are shown in FIG. Based on the above results, the cyclic voltammogram was measured under conditions in which the working electrode was changed from a platinum wire to a copper wire and no redox agent was included. The results are shown in Figure 8a. For comparison, a cyclic voltammogram was measured using sodium tetraphenylborate in acetonitrile as a supporting salt, and the results are shown in FIG. 8b. Similarly, using a zinc wire as the working electrode, the cyclic voltammogram was measured in the above solution composition, and the results are shown in FIG. 9a. For comparison, a cyclic voltammogram was measured using sodium tetraphenylborate in acetonitrile as a supporting salt, and the results are shown in FIG. 9b. Similarly, FIG. 10 shows the results of measuring the cyclic voltammogram in the above solution composition using a silver wire as the working electrode. Considering the above measurement results, the electrolytic solution according to the present invention is significantly different from conventional electrolytic solutions, and the dissolution of the metal salt into the electrolytic solution is controlled to strongly reflect the stability of complex formation with the crown compound. ing. Therefore, for this reason, a number of specific applications of the present invention from (A) to (E) above are possible. That is, as can be seen from the above examples, benzene, a non-polar solvent that could not be used in conventional electrochemical systems, is involved in the structure of the electrochemical system, and in this new electrochemical system, copper electrodes and zinc electrodes are used. It has become clear that the stable potential range of is extended to the decomposition potential of this electrolyte. On the other hand, in the silver electrode, silver ions are 15-crown-5
Reflecting the fact that a strong complex is formed between the two, it elutes into the electrolyte at zero overvoltage. From the above results, it is clear that the electrolytic solution according to the present invention has an elution order that is opposite to the normal ionization tendency, and a novel metal refining method as shown in (B) above is constructed. Furthermore, it goes without saying that new technologies such as (A) and (C) above can be constructed. Example 2 Benzene, a non-polar solvent, and 15-crown-5, whose pore radius is approximately equal to the ionic radius of sodium, were mixed so that the molar fraction of benzene was 0.8, and sodium tetraphrase was added to the mixture. An electrolytic solution was prepared by adding enylborate to a concentration of 0.1M. First, a single crystal of cadmium sulfide is coated with an indium-gallium alloy, and then a copper wire is connected using silver paste to create an ohmic junction.
Only one side of the crystal was left exposed to the electrolyte, and the other side was filled with epoxy resin to fix the electrode on a glass substrate. The above electrode was used as the working electrode, the platinum electrode was used as the counter electrode, and the silver wire was used as the reference electrode.These three electrodes were immersed in the above electrolyte solution and cyclically operated using a potentiometer under dark conditions and under light excitation conditions using a 500W xenon lamp. A voltammogram was measured. The measurement results showed that under dark conditions, cathode current was observed only when the electrode potential relative to the silver wire was less noble than -0.9V, and no current was observed when it was nobler than -0.9V. On the other hand, under optical excitation conditions using a xenon lamp, -
Although cathode current is observed from 0.9V, −
At a potential higher than 0.6 V, an anodic current that was not observed under dark conditions was newly observed. It was also found that this anode current quickly disappeared when the excitation light was cut off, and was quickly recovered when the excitation light was introduced again. Based on the above results, we fixed the electrode potential at 1.0 V with respect to the silver wire and investigated the temporal behavior of the photocurrent generated by excitation light. As a result, a photocurrent of 1.6 mA/cm ² was measured at the initial stage of photosensitization electrolysis, and this continued to flow with almost no attenuation even after continuous photosensitization electrolysis for more than 6 hours. Since the CdS photoanode was found to be stable, a photovoltaic cell was assembled using this semiconductor electrode and a platinum electrode. FIG. 11 shows the state of the photovoltaic cell at this time. Insert each electrode into both sides of the U-shaped tube, and gently insert the cadmium sulfide single crystal electrode from above.
An electrolytic solution having the composition described above was injected, while a sulfuric acid acidic saturated sodium chloride aqueous solution was injected from the opposite platinum electrode side. Both electrolytes were separated into two phases and contacted each other. When both electrodes were single-circuited and the cadmium sulfide single crystal electrode was photoexcited with a 500WXe lamp, a photocurrent flowed through the external circuit and hydrogen bubbles were generated from the platinum electrode. Second, a zinc oxide semiconductor electrode was made by pressure firing zinc oxide powder using the same method as described for the cadmium sulfide single crystal above, and a platinum counter electrode,
The three silver reference electrodes were immersed in an electrolytic solution with the same composition as the cadmium sulfide electrode, and cyclic voltammograms were measured under potential regulation conditions using a potentiostat in the dark and under light excitation conditions using a 500w Xe lamp. . The results showed that under dark conditions, a cathodic current was observed in the potential range less noble than -0.3V, and in the electrical potential region more noble than -0.2V, a photosensitizing current that was not observed under dark conditions flowed as an anode current. . Third, use n-type silicon as an electrode in exactly the same manner as described in the first and second sections above, and use three electrodes, a platinum counter electrode and a silver reference electrode, in exactly the same manner as in the first and second sections. The samples were immersed in the same electrolyte solution, and cyclic voltammograms were measured under potential control conditions using a potentiostat, under dark conditions, and under photoexcitation conditions using a 500w Xe lamp. Next, the potential of the n-type silicon electrode was fixed at +1.7V, and the light from a 500w Xe lamp was picked up to examine the change in photocurrent over time. When photosensitized electrolysis was carried out continuously for 2 hours, it was confirmed that the electrolyte was significantly more stable than ordinary electrolytes.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the state of an n-type semiconductor-electrolyte-metal counter electrode. Figure 2 shows the decomposition potential of an n-type semiconductor.
FIG. 3 is a diagram showing the stability and instability of a semiconductor electrode depending on the level of Ed and water oxidation potential Eo. Figure 3 shows CdS
FIG. 3 is a diagram showing the dependence of the dissolution inhibition rate on the redox potential of the reducing agent. FIG. 4 is a diagram showing redox agents that can stabilize an unstable semiconductor electrode and redox agents that cannot. Figure 5 shows 15
FIG. 3 is a diagram showing the dielectric constants of solutions with different compositions of Crown-5 and benzene. FIG. 6 is a diagram showing the electrical conductivity of the solution when the concentration of the supporting salt is changed. FIGS. 7 to 10 are diagrams showing the measurement results of cyclic voltammograms. FIG. 11 is a diagram showing the apparatus used in Example 2. In FIG. 11, the numbers indicate the following. DESCRIPTION OF SYMBOLS 1... Cadmium sulfide single crystal electrode, 2... Platinum electrode, 3... Electrolyte of the present invention, 4... Sulfuric acid acidic saturated sodium chloride aqueous solution, 5... Load, 6...
Voltmeter, 7... generated hydrogen, 8... excitation light.

Claims (1)

[Claims] 1. An electrolytic solution comprising a solution of a crown compound holding cations and a low polar solvent, and containing substantially no polar solvent.